A substantial body of literature has been developed concerning techniques that employ binding reactions, e.g., antigen-antibody reactions, nucleic acid hybridization and receptor-ligand reactions, for the sensitive measurement of analytes of interest in samples. The high degree of specificity in many biochemical binding systems has led to many assay methods and systems of value in a variety of markets including basic research, human and veterinary diagnostics, environmental monitoring and industrial testing. The presence of an analyte of interest may be measured by directly measuring the participation of the analyte in a binding reaction. In some approaches, this participation may be indicated through the measurement of an observable label attached to one or more of the binding materials.
While the sandwich immunoassay format provides excellent sensitivity and specificity in many applications, some analytes are present at concentrations that are too low for detection by conventional immunoassay techniques. The performance of sandwich immunoassays can also be limited by the non-specific binding of detection antibodies and by the instability of sandwich complexes comprising high off-rate antibodies. However, efforts to modify conventional immunoassay techniques to improve sensitivity and specificity often yield more complex, labor intensive protocols that can be hampered by inefficiencies at each step that can greatly impact the sensitivity and specificity of an assay. For example, in a complex assay requiring multiple binding events and/or reactions, if any one event or reaction is less than optimal, the sensitivity and specificity of the overall assay can suffer. There is a need for new techniques for improving sandwich immunoassay performance by improving sensitivity, reducing non-specific binding and improving the stability of sandwich complexes.